我正在用python编写一些C API的包装。我能够编写包装器,并且当我尝试从另一个程序调用该包装器以访问API时,指针变量更改后的值不会在python变量中得到更新。
我来自pythonWrapper.py的API代码:
import ctypes
from enum import Enum
_obj = cdll.LoadLibrary(./sharedObj.so)
#some enums and structure will be here like :
class structwrap(Structure):
_fields_ = [("id", c_int),
("type", c_int),
("state", c_int)]
def __init__(self):
self.id = 0
self.type = 0
self.state = 0
def wrappedAPI(structwrapList, count):
_obj.wrappedAPI.argtypes = [ctypes.POINTER(structwrapList),ctypes.POINTER(c_int)]
_obj.wrappedAPI.restype = int
if not structwrapList:
structwrapList = structwrap()
ret = _obj.orgAPI(byref(structwrapList),byref(c_int(count)))
print (count)
return ret
相应的C代码是:
typedef struct structOrg
{
int id; /* index */
dvDevIcType_t type; /* type */
dvDevExecState_t state; /* state */
}structOrg_t;
int orgAPI(structOrg_t *structList, int *count){
...
//count value is being changed here. like count = count+1
}
上面的python文件被从test.py调用:
from ctypes import *
from pythonWrapper import *
count =0
ret = dvDeviceGet(None, count)
print (count)
输出ret成功,但count值仍为0,但在c函数中将其更改为2。但是在python变量中,它仍为0。
有人可以在这里指出我的错误吗?
答案 0 :(得分:1)
byref(c_int(count))
创建一个新的c_int
并将一个指针传递给那个。 count
不受影响。 count
是普通的Python int,不是C int或C int的包装对象。
答案 1 :(得分:0)
一些重构:
_obj = cdll.LoadLibrary(./sharedObj.so)
# Only need to do this once, not every time inside the function
_obj.wrappedAPI.argtypes = [ctypes.POINTER(structwrapList),ctypes.POINTER(c_int)]
_obj.wrappedAPI.restype = ctypes.c_int # Needs to be a ctypes type.
def wrappedAPI(structwrapList,count):
if not structwrapList:
structwrapList = structwrap()
c_count = ctypes.c_int(count) # Create a ctypes type to pass by reference
ret = _obj.orgAPI(byref(structwrapList),ctypes.byref(c_count))
return ret,c_count.value
致电:
ret,count = dvDeviceGet(None, count)